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Does Thunder Really Only Happen When It's Raining?

By Renny Vandewege


According to Fleetwood Mac's hit song, "Dreams," thunder only happens when it's raining. Sure, it's just a line from a song, but is there anything to it?

In Stevie Nicks' world, maybe. The atmosphere, however, sings a different lyric. Thunder can occur during snowstorms, volcanic eruptions, forest fires, dry thunderstorms and in clear blue skies, none of which includes rain falling to the ground.

In its most common occurrence, thunder is a result of lightning striking inside a cumulonimbus cloud - a tall, puffy cloud resembling cauliflower that forms when the atmosphere is unstable. Cumulonimbus clouds are often referred to as "thunderheads" for their unique shape and their association with producing thunder. As a cumulonimbus cloud intensifies, it becomes charged with positive electrical charges. Those charges connect to negative charges along the ground and create an intense current of electricity we know as lightning.

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Each lightning strike can be as hot as 55,000 degrees F, over five times as hot as the surface of the sun. This intense heat causes the air to rapidly expand, which forms a sonic sound wave that travels through the atmosphere in the form of thunder.

Although most of us hear thunder only when it's raining, science provides brilliant forms of lightning and thunder in cases where no rain is present.

Snow and thunder seem like the least likely of weather marriages but find themselves paired together in rare situations. During major snowstorms, enough atmospheric instability exists to allow the air to rise similar to that of a thunderstorm, causing the electrical charges to be present and lightning to strike. The thunder, however, sounds much different during cases of "thundersnow," as snow acts to dampen the accoustics. This limits the sound of thunder from traveling farther than three miles from the lightning strike, as opposed to over 10 miles in a typical thunderstorm. In cases of thundersnow, snowfall rates may exceed 2 inches of accumulation per hour, thanks to the added instability in the atmosphere. The combination of thunder and intense snow accumulation makes thundersnow a cool story for those lucky enough to experience it.

In the rare event you find yourself staring down an erupting volcano, chances are that you could hear thunder admist the roaring sound of magma blasting onto the landscape. During explosive volcanic eruptions, incredible amounts of heat cause particles to be lofted into the atmosphere. These particles acquire high levels of electrical charge during the eruption process and become separated when rising in the atmosphere. Volcanoes are known to be prolific lightning and thunder producers, though few people are often close enough to see or hear the thunder due to the danger of the volcano eruption itself. Instead, scientists are relegated to using lightning detection technology to detect lightning strikes within the eruption. Occasionally, photographers have been able to capture stunning pictures of volcano lightning.

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Forest fires are commonplace to those in the western United States and are another inducer of unique forms of thunder and lightning. Within forest fires, intense heat from burning trees and vegetation rise and create a pyrocumulonimbus cloud - a cumulonimbus cloud formed directly in the smoke of a fire.

One leading cause of forest fires is lightning itself. Not all thunderstorms produce rain that hits the ground. In the desert southwest, including Arizona and New Mexico, thunderstorms form during the summer months in an atmosphere characterized by warm and humid conditions above the ground but hot and dry conditions at the surface of the earth. This results in thunderstorms forming with cloud bases up to two miles above the ground. Rain forms as normal but falls into an extremely dry atmosphere, evaporating any trace of rain before it hits the parched ground. These are most commonly known as "dry thunderstorms" and are a major headache to firefighters in the southwest.

Bolts from the blue may be the scariest form of thunder and lightning, and they appear when least expected. These bolts of lightning strike after rain has ended and tend to come out of the back side of the thunderstorm. They have been known to strike as far as 25 miles away from the parent thunderstorm. They are termed "bolts from the blue" as they appear to strike in areas of clear blue sky. This is why meteorologists suggest waiting at least 30 minutes from the last rumble of thunder before venturing outside.

Of course, I don't think Stevie Nicks was too concerned with the science of weather when she wrote the song, and that's just fine.

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